"Gentlemen's Tuck" (as I've heard it called) -- What the original post mentioned. Casually leaning forward, arms along the sides, hands behind the rear. Poles can either drag or point at rakish angle of your choosing. The purpose is to strike a relatively aerodynamic position while not actually tucking, as a real tuck scares the ski patrol and makes it look like you're trying too hard.
"Turkey Tuck" (that's as a good a name as any) -- Knees bent into a nearly seated position, with calves hard against the back of the boots; bent over at the waist enough to be uncomfortable, but with the shoulders up; hands tucked in around the groin, poles under the armpits, ideally angled up at more than 45 degrees. For extra points, should be executed in a lopsided gliding wedge.
"Tuck" -- Back parallel to the snow; hands out in front; elbows in the vicinity of the knees. This position alone is enough to get you warned for skiing too fast at some areas.